Using RNAseq to dissect virulence factors of wheat and barley pathogen Bipolaris sorokiniana

Bipolaris sorokiniana is a hemibiotrophic pathogen causing spot blotch (SB) and common root rot (CRR) in both wheat and barley, and is causal to significant yield and economic losses. As a hemibiotroph, B. sorokiniana displays a rapid switch in lifecycle from biotrophic to necrotrophic growth during the early stages of infection, ultimately resulting in the death of host tissue. Despite the great significance of B. sorokiniana, the molecular mechanisms underpinning disease are poorly understood. Therefore, in this study, I sought to identify host specific virulence factors that facilitate pathogenicity in the different cereal hosts and to dissect the underlying mechanisms. A deep RNA sequencing approach was undertaken from wheat and barley leaves infected with B. sorokiniana. In this dataset, I found fungal genes encoding small secreted proteins (SSPs), secondary metabolites (SMs), and cell wall-degrading enzymes that showed strongly differentiated transcriptional profiles between the two hosts and at different stages of the infections. Based on the transcriptomic datasets and machine-learning bioinformatics prediction approaches, ten novel SSP effector candidates which were significantly differentially expressed between wheat and barley infections were identified. Further functional characterisation of these ten SSP effector candidates were employed through homologue recombination approach of protoplast transformation. Additionally, seedling pathogenicity assays were applied to confirm whether the mutants the of SSP effector candidates were required for the virulence of B. sorokiniana. Unfortunately, no significant difference in disease symptoms was observed between mutants and wild type in both wheat and barley, suggesting that all ten effector candidates were not required for the virulence of B. sorokiniana as assessed by this seedling in planta assay. The expression profile of SMs were also analysed. Among them, a siderophore synthase gene Chr04.426 was highly expressed at the early timepoint of both the barley and wheat infections. Further functional characterisation showed that the gene disruption mutants of Chr04.426 could significantly reduce disease symptoms in both wheat and barley compared to wild type. These findings indicate that Chr04.426 plays an important role in the pathogenicity of B. sorokiniana. Additionally, Chr04.426 is also crucial iron uptake ability of B. sorokinina. Overall, Chr04.426 is required for the siderophore-mediated iron uptake and virulence of B. sorokiniana. To date, the virulence determinants of B. sorokiniana have remained poorly understood. In this study, in planta transcriptome expression profile provides a broad dynamic view of the expression level of SSPs, SMs and cell wall-degrading enzymes of B. sorokiniana during infection between wheat and barley. Furthermore, in this dataset, a nonribosomal peptide synthase Chr04.426, which was highly expressed in early infection timepoint of both wheat and barley, was identified to be involved in siderophore-mediated iron uptake and virulence of B. sorokiniana. Collectively, these data have fundamentally advanced our understanding of the interaction between B. sorokiniana-wheat/ barley during infection

Involvement of FvSet1 in Fumonisin B1 Biosynthesis, Vegetative Growth, Fungal Virulence, and Environmental Stress Responses in Fusarium verticillioides

Fusarium verticillioides (teleomorph, Gibberella moniliformis) is an important plant pathogen that causes seedling blight, stalk rot, and ear rot in maize (Zea mays). During infection, F. verticillioides produce fumonsins B1 (FB1) that pose a serious threat to human and animal health. Recent studies showed that Set1, a methyltransferase of H3K4, was responsible for toxin biosynthesis in filamentous fungi. However, to date, the regulation of FvSet1 on FB1 biosynthesis remains unclear. In the current study, we identified only one Set1 ortholog in F. verticillioides (FvSet1) and found that the deletion of FvSET1 led to various defects in fungal growth and pathogenicity. More interestingly, the FvSET1 deletion mutant (ΔFvSet1) showed a significant defect in FB1 biosynthesis and lower expression levels of FUM genes. FvSet1 was also found to play an important role in the responses of F. verticillioides to multiple environmental stresses via regulating the phosphorylation of FvMgv1 and FvHog1. Taken together, these results indicate that FvSet1 plays essential roles in the regulation of FB1 biosynthesis, fungal growth and virulence, as well as various stress responses in F. verticillioides